
I think Fineas mental age has been greatly affected by being stuck as a child. It's not really a suprise that she started to be very playful and curious, even the spirits noticed that (was mentioned in the ceremony chapter I think).
If that was not the case then yes, it would be weird if she liked him that early on.. as a 5 year old. Lol
The dynamic between the maid and Lesian is so cute :( Sadly they took the B from Lesian so that won't happen